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Table of Contents
glTexEnvf, glTexEnvi, glTexEnvfv, glTexEnviv - set texture environment parameters
void glTexEnvf( GLenum target,
GLenum pname,
GLfloat param )
void glTexEnvi( GLenum target,
GLenum pname,
GLint param )
eqn not supported
- target
- Specifies a texture environment. Must
be GL_TEXTURE_ENV.
- pname
- Specifies the symbolic name of a single-valued texture
environment parameter. Must be GL_TEXTURE_ENV_MODE.
- param
- Specifies a single
symbolic constant, one of GL_MODULATE, GL_DECAL, GL_BLEND, or GL_REPLACE.
void glTexEnvfv( GLenum target,
GLenum pname,
const GLfloat *params )
void glTexEnviv( GLenum target,
GLenum pname,
const GLint *params )
- target
- Specifies a texture environment. Must be GL_TEXTURE_ENV.
- pname
- Specifies the symbolic name of a texture environment parameter. Accepted
values are GL_TEXTURE_ENV_MODE and GL_TEXTURE_ENV_COLOR.
- params
- Specifies
a pointer to a parameter array that contains either a single symbolic constant
or an RGBA color.
A texture environment specifies how texture
values are interpreted when a fragment is textured. target must be GL_TEXTURE_ENV.
pname can be either GL_TEXTURE_ENV_MODE or GL_TEXTURE_ENV_COLOR.
If pname
is GL_TEXTURE_ENV_MODE, then params is (or points to) the symbolic name
of a texture function. Four texture functions may be specified: GL_MODULATE,
GL_DECAL, GL_BLEND, and GL_REPLACE.
A texture function acts on the fragment
to be textured using the texture image value that applies to the fragment
(see glTexParameter) and produces an RGBA color for that fragment. The following
table shows how the RGBA color is produced for each of the three texture
functions that can be chosen. $C$ is a triple of color values (RGB) and
$A$ is the associated alpha value. RGBA values extracted from a texture
image are in the range [0,1]. The subscript $f$ refers to the incoming fragment,
the subscript $t$ to the texture image, the subscript $c$ to the texture
environment color, and subscript $v$ indicates a value produced by the
texture function.
A texture image can have up to four components per texture
element (see glTexImage1D, glTexImage2D, glTexImage3D, glCopyTexImage1D,
and glCopyTexImage2D). In a one-component image, $L sub t$ indicates that
single component. A two-component image uses $L sub t$ and $A sub t$. A three-component
image has only a color value, $C sub t$. A four-component image has both
a color value $C sub t$ and an alpha value $A sub t$.
| Base internal | Texture
functions |
| GL_MODULATE | GL_DECAL | GL_BLEND | GL_REPLACE |
| GL_ALPHA | $C sub v
~=~ C sub f$ | undefined | $C sub v ~=~ C sub f$ | $C sub v ~=~ C sub f$ |
| | $A sub
v ~=~ A sub f A sub t$ | | $A sub v ~=~ A sub f$ | $A sub v ~=~ A sub t$ |
| GL_LUMINANCE | $C
sub v ~=~ L sub t C sub f$ | undefined | $C sub v ~=~ ( 1 - L sub t ) C sub f$ | $C
sub v ~=~ L sub t$ |
| | | $+ L sub t C sub c$ |
| 1 | $A sub v ~=~ A sub f$ | | $A sub v
~=~ A sub f$ | $A sub v ~=~ A sub f$ |
| GL_LUMINANCE | $C sub v ~=~ L sub t C sub
f$ | undefined | $C sub v ~=~ ( 1 - L sub t ) C sub f $ | $C sub v ~=~ L sub t$ |
| \f3_ALPHA |
| | $+ L sub t C sub c$ |
| 2 | $A sub v ~=~ A sub t A sub f$ | | $A sub v ~=~ A sub t
A sub f$ | $A sub v ~=~ A sub t$ |
| GL_INTENSITY | $C sub v ~=~ C sub f I sub t$ | undefined | $C
sub v ~=~ ( 1 - I sub t ) C sub f$ | $C sub v ~=~ I sub t$ |
| | | $+ I sub t C sub
c$ |
| c | $A sub v ~=~ A sub f I sub t$ | | $A sub v ~=~ ( 1 - I sub t ) A sub f $ | $A
sub v ~=~ I sub t$ |
| | | $+ I sub t A sub c$ |
| GL_RGB | $C sub v ~=~ C sub t C sub
f$ | $C sub v ~=~ C sub t$ | $C sub v ~=~ (1 - C sub t) C sub f $ | $C sub v ~=~
C sub t$ |
| | | $+ C sub t C sub c$ |
| 3 | $A sub v ~=~ A sub f$ | $A sub v ~=~ A sub
f$ | $A sub v ~=~ A sub f$ | $A sub v ~=~ A sub f$ |
| GL_RGBA | $C sub v ~=~ C sub
t C sub f$ | $C sub v ~=~ ( 1 - A sub t ) C sub f $ | $C sub v ~=~ (1 - C sub t)
C sub f $ | $C sub v ~=~ C sub t$ |
| | $+ A sub t C sub t$ | $+ C sub t C sub c$ |
| 4 | $A
sub v ~=~ A sub t A sub f$ | $A sub v ~=~ A sub f$ | $A sub v ~=~ A sub t A sub
f$ | $A sub v ~=~ A sub t$ |
If pname is GL_TEXTURE_ENV_COLOR, params is a
pointer to an array that holds an RGBA color consisting of four values.
Integer color components are interpreted linearly such that the most positive
integer maps to 1.0, and the most negative integer maps to -1.0. The values
are clamped to the range [0,1] when they are specified. $C sub c$ takes
these four values.
GL_TEXTURE_ENV_MODE defaults to GL_MODULATE and GL_TEXTURE_ENV_COLOR
defaults to (0, 0, 0, 0).
GL_REPLACE may only be used if the GL version
is 1.1 or greater.
Internal formats other than 1, 2, 3, or 4 may only be
used if the GL version is 1.1 or greater.
When the GL_ARB_multitexture extension
is supported, glTexEnv controls the texture environment for the current
active texture unit, selected by glActiveTextureARB. GL_INVALID_ENUM is
generated when target or pname is not one of the accepted defined values,
or when params should have a defined constant value (based on the value
of pname) and does not.
GL_INVALID_OPERATION is generated if glTexEnv is
executed between the execution of glBegin and the corresponding execution
of glEnd.
glGetTexEnv
glActiveTextureARB(3G)
, glCopyPixels(3G)
,
glCopyTexImage1D(3G)
, glCopyTexImage2D(3G)
, glCopyTexSubImage1D(3G)
, glCopyTexSubImage2D(3G)
,
glCopyTexSubImage3D(3G)
, glTexImage1D(3G)
, glTexImage2D(3G)
, glTexImage3D(3G)
,
glTexParameter(3G)
, glTexSubImage1D(3G)
, glTexSubImage2D(3G)
, glTexSubImage3D(3G)
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